These types of backpacks with a continuous back length adjustment are known, for example, from EP 1 602 299 A1 or from EP 0 122 764 A2.
In the EP 1 602 299 A1, a yoke plate, attached to the two shoulder straps, slides along two rods, when the shoulder straps' height is adjusted. The yoke plate can be pulled down by means of a strap. The strap is guided through a passageway, which is formed in a back plate of the rucksack. A toothed strip is arranged at one end of the strap, which can be gripped by a user of the rucksack. This toothed strip can be arrested by means of a locking mechanism.
One disadvantage to be considered here is that the yoke plate is, in fact, prevented from moving upward in this type of back length adjustment. It is, however, possible to move the yoke plate downward, however, when the toothed strip is arrested in the locking mechanism. Furthermore, this type of adjustment mechanism is relatively stiff, because the strap is threaded through the passage in the back plate and must therefore overcome significant friction forces.
In the rucksack described in EP 0 122 764 A2, scapula pads of the shoulder straps on the rucksack are arranged along a transverse plate, which is movable along two vertical frame members. Runners are arranged on the frame members to which straps are mounted to move the transverse plate. The runners are mounted on the frame members so tightly that they can only be moved when force is applied.
In this rucksack as well, the mechanism for the back length adjustment must be stiff.
What is needed then is a rucksack of the type described above in which the continuous back length adjustment can be carried out in a particularly easy and smooth manner.